Antenna Device and Electronic Equipment

ABSTRACT

According to one embodiment, an antenna device includes a short circuit path, a first open-ended element, a feed side element, a second open-ended element, and a short circuit element. One end of the short circuit path is connected to a ground point near a feed point. The first open-ended element extends from another end of the short circuit path. The feed side element extends from near the feed point in a direction in which the first open-ended element extends with an edge close to ground. The second open-ended element extends from near an end of the feed side element in the direction in which the first open-ended element extends. The short circuit element connects between an end of the first open-ended element and a point on an edge of the feed side element opposite the edge close to the ground or a point on the second open-ended element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2008-195529, filed Jul. 29, 2008, theentire contents of which are incorporated herein by reference.

BACKGROUND

1. Field

One embodiment of the invention relates to an antenna device andelectronic equipment.

2. Description of the Related Art

Recently, instead of whip antennas that have been widely used, built-inantennas are increasingly being used as wireless communication antennasfor electronic equipment capable of wireless communication such asnotebook personal computers (PCs). Such a built-in antenna has antennaelements built in the housing, and therefore is easily handled when usedor stored compared to the whip antenna. Moreover, the housing can bedesigned more flexibly.

In electronic equipment having a built-in antenna, due to theminiaturization of the housing, it is often the case that the antennaelements are arranged near metal part such as peripheral circuitsmounted on the circuit board. This may lower the input impedance of theantenna and thus may cause an impedance mismatch between the antenna andthe feed circuit, resulting in degraded performance.

Accordingly, a folded monopole antenna is used to prevent a decrease inthe input impedance of the built-in antenna.

With the folded monopole antenna, the input impedance of the antenna canbe increased compared to that of a monopole antenna, and can also beadjusted by the ratio between the diameters of parallel lines. On theother hand, the folded monopole antenna is likely to be larger than amonopole antenna, and therefore requires elaborate arrangement, such asto wire the antenna elements in three dimensions, to be built in smallelectronic equipment.

Japanese Patent Application Publication (KOKAI) No. 2003-158419discloses a conventional technology that enables resonance to occur at aplurality of resonant frequencies by adding an antenna to a conventionalinverted-F antenna.

FIG. 50 is a schematic diagram of an antenna designed referring to thebasic structure of an inverted-F antenna according to the conventionaltechnology. As illustrated in FIG. 50, the inverted-F antenna comprisesa radiation conductor (36 mm) 1, a ground conductor 2, a short circuitelement (8 mm) 3, a feed line 5, and a feed conductor (80 mm) 6. Theradiation conductor 1 is located opposite the ground conductor 2. Theshort circuit element 3 connects between the radiation conductor 1 andthe ground conductor 2. The feed line 5 extends between the radiationconductor 1 and the ground conductor 2 and is connected to a feed point4 spaced apart by 1 mm from a ground point at which the short circuitelement 3 is connected to the ground conductor 2. The feed conductor 6is connected to the feed line 5. The radiation conductor 1 and the feedconductor 6 are supplied with power via the feed line 5.

FIG. 51 is a Smith chart of the impedance variation of the inverted-Fantenna illustrated in FIG. 50. The Smith chart of FIG. 51 representsvariations in the input impedance of the inverted-F antenna when thefrequency signal fed from the feed point 4 is changed in a range of 700to 2500 MHz. As illustrated in FIG. 51, the plot of the impedance of theinverted-F antenna deviates upward from the centre of the Smith chart,i.e., 50Ω.

This is because the inductivity of the input impedance increases due tocurrent flowing from the feed point 4 to the ground point as indicatedby an arrow in FIG. 50. As a result, an impedance mismatch may occur ata desired frequency band.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A general architecture that implements the various features of theinvention will now be described with reference to the drawings. Thedrawings and the associated descriptions are provided to illustrateembodiments of the invention and not to limit the scope of theinvention.

FIG. 1 is an exemplary perspective view of a notebook PC according to afirst embodiment of the invention;

FIG. 2 is an exemplary schematic diagram of the circuitry of thenotebook PC in the first embodiment;

FIG. 3 is an exemplary schematic diagram of an antenna device in thefirst embodiment;

FIG. 4 is an exemplary schematic diagram for explaining the operationprinciple of a short circuit path and a first open-ended element in thefirst embodiment;

FIG. 5 is an exemplary schematic diagram for explaining the operationprinciple of a feed side element, a short circuit element, and the firstopen-ended element in the first embodiment;

FIG. 6 is an exemplary schematic diagram for explaining the operationprinciple of the short circuit path, the short circuit element, and asecond open-ended element in the first embodiment;

FIG. 7 is an exemplary schematic diagram for explaining the operationprinciple of the feed side element and the second open-ended element inthe first embodiment;

FIG. 8 is an exemplary diagram of a specific form of an analytical modelin the first embodiment;

FIG. 9 is an exemplary diagram of a form of a ground conductor of theanalytical model in the first embodiment;

FIG. 10 is an exemplary Smith chart of the antenna characteristics ofthe analytical model of FIGS. 8 and 9 in the first embodiment;

FIGS. 11 to 14 are exemplary schematic diagrams for explaining anantenna realized by the analytical model of FIGS. 8 and 9 in the firstembodiment;

FIG. 15 is an exemplary Smith chart of the antenna characteristics ofthe analytical model having the feed side element and one not having thefeed side element in the first embodiment;

FIG. 16 is an exemplary schematic diagram for explaining current flow inthe analytical model having the feed side element in the firstembodiment;

FIG. 17 is an exemplary schematic diagram for explaining current flow inthe analytical model not having the feed side element in the firstembodiment;

FIG. 18 is an exemplary schematic diagram of an antenna device accordingto a modification of the first embodiment;

FIG. 19 is an exemplary schematic diagram of an analytical model of anantenna device comprising a short circuit path in a second embodiment ofthe invention;

FIG. 20 is an exemplary schematic diagram of an analytical model of anantenna device having no short circuit path in the second embodiment;

FIG. 21 is an exemplary Smith chart of the antenna characteristics ofthe analytical models of FIGS. 19 and 20 in the second embodiment;

FIG. 22 is an exemplary schematic diagram of an antenna device accordingto a third embodiment of the invention;

FIG. 23 is an exemplary diagram of a specific form of an analyticalmodel in the third embodiment;

FIG. 24 is an exemplary Smith chart of the antenna characteristics ofthe analytical model of FIG. 23 in the third embodiment;

FIG. 25 is an exemplary schematic diagram of an antenna device accordingto a fourth embodiment of the invention;

FIGS. 26 to 28 are exemplary diagrams of specific forms of analyticalmodels in the fourth embodiment;

FIG. 29 is an exemplary schematic diagram for explaining resonance thatoccurs in the analytical model of FIG. 26 in the fourth embodiment;

FIG. 30 is an exemplary schematic diagram for explaining resonance thatoccurs in the analytical model of FIG. 27 in the fourth embodiment;

FIG. 31 is an exemplary graph of results of analysis on VSWRcharacteristics over a first resonant frequency band in the analyticalmodels of FIGS. 26 to 28 in the fourth embodiment;

FIG. 32 is an exemplary schematic diagram of an antenna device accordingto a fifth embodiment of the invention;

FIG. 33 is an exemplary diagram of a specific form of an analyticalmodel in the fifth embodiment;

FIG. 34 is an exemplary Smith chart of the antenna characteristics ofthe analytical model of FIG. 33 in the fifth embodiment;

FIG. 35 is an exemplary schematic diagram of an antenna device accordingto a sixth embodiment of the invention;

FIG. 36 is an exemplary diagram of an analytical model of the antennadevice comprising a parasitic element in the sixth embodiment;

FIG. 37 is an exemplary graph of results of analysis on VSWRcharacteristics of an analytical model having no parasitic element andone having the parasitic element in the sixth embodiment;

FIG. 38 is an exemplary Smith chart of the antenna characteristics of ananalytical model having the parasitic element and one not having theparasitic element in the sixth embodiment;

FIG. 39 is an exemplary schematic diagram of an antenna devicecomprising a short circuit path having a projection in the seventhembodiment;

FIG. 40 is an exemplary diagram of a specific form of an analyticalmodel of the antenna device of FIG. 39 in the seventh embodiment;

FIG. 41 is an exemplary Smith chart of the antenna characteristics ofthe analytical model of FIG. 40 in the seventh embodiment;

FIG. 42 is an exemplary schematic diagram of an antenna devicecomprising a short circuit path provided with an impedance matchingcircuit thereon in the eighth embodiment;

FIG. 43 is an exemplary diagram of a specific form of an analyticalmodel of the antenna device comprising the short circuit path providedwith a chip inductor thereon in the eighth embodiment;

FIG. 44 is an exemplary Smith chart of the antenna characteristics ofthe analytical model of FIG. 43 in the eighth embodiment;

FIGS. 45A to 45L are exemplary schematic diagrams of antenna devicesaccording to modifications of the first to seventh embodiments;

FIG. 46 is an exemplary diagram of a specific form of an antenna devicein an embodiment;

FIG. 47 is an exemplary graph of results of analysis on VSWRcharacteristics of the antenna device of FIG. 46 in the embodiment;

FIG. 48 is an exemplary diagram of a specific form of an antenna devicein another embodiment;

FIG. 49 is an exemplary graph of results of analysis on VSWRcharacteristics of the antenna device of FIG. 48 in the embodiment;

FIG. 50 is an exemplary schematic diagram of an antenna designedreferring to the basic structure of an inverted-F antenna according to aconventional technology; and

FIG. 51 is an exemplary Smith chart of the impedance variation of theinverted-F antenna illustrated in FIG. 50.

DETAILED DESCRIPTION

Various embodiments according to the invention will be describedhereinafter with reference to the accompanying drawings. In general,according to one embodiment of the invention, an antenna devicecomprises: a short circuit path a first end of which is connected to aground point that is located near a feed point; a first open-endedelement that has a second end being open, and extends from a second endof the short circuit path; a feed side element that extends from nearthe feed point in a direction in which the first open-ended elementextends to have an edge close to ground; a second open-ended elementthat has a second end being open, and extends from near a second end ofthe feed side element in the direction in which the first open-endedelement extends; and a short circuit element that connects between afirst end of the first open-ended element and either a point on an edgeof the feed side element opposite the edge close to the ground or apoint on the second open-ended element. A length, from the feed pointthrough an outer edge of the feed side element including the edge closeto the ground and the short circuit element to the second end of thefirst open-ended element, is substantially a quarter of a wavelength ofa first resonant frequency. A length, from the feed point through theouter edge of the feed side element including the edge close to theground to the second end of the second open-ended element, issubstantially a quarter of a wavelength of a second resonant frequency.

According to another embodiment of the invention, electronic equipmentcomprises a housing having a built-in antenna device. The antenna devicecomprises: a short circuit path a first end of which is connected to aground point that is located near a feed point; a first open-endedelement that has a second end being open, and extends from a second endof the short circuit path; a feed side element that extends from nearthe feed point in a direction in which the first open-ended elementextends to have an edge close to ground; a second open-ended elementthat has a second end being open, and extends from near a second end ofthe feed side element in the direction in which the first open-endedelement extends; and a short circuit element that connects between afirst end of the first open-ended element and either a point on an edgeof the feed side element opposite the edge close to the ground or apoint on the second open-ended element. A length, from the feed pointthrough an outer edge of the feed side element including the edge closeto the ground and the short circuit element to the second end of thefirst open-ended element, is substantially a quarter of a wavelength ofa first resonant frequency. A length, from the feed point through theouter edge of the feed side element including the edge close to theground to the second end of the second open-ended element, issubstantially a quarter of a wavelength of a second resonant frequency.

With reference to FIG. 1, the configuration of a notebook PC accordingto a first embodiment of the invention will be schematically described.In the following embodiments, electronic equipment is described as anotebook PC with a built-in antenna device, and an antenna device isdescribed as being applied to such a notebook PC. However, this is byway of example only. The electronic equipment may be of other types suchas, for example, a personal digital assistant and a mobile phone with abuilt-in antenna device, and also the antenna device may be applied tothem. FIG. 1 is a perspective view of a notebook PC 100 according to thefirst embodiment.

As illustrated in FIG. 1, the notebook PC 100 comprises a display module101 and a main body 102. The display module 101 is a liquid crystaldisplay (LCD) comprising a LCD panel 103. The display module 101comprises, above the LCD panel 103, an antenna device 104 for wirelesscommunication. The display module 101 and the main body 102 areconfigured to rotate freely on a hinge 105 between an open position anda closed position.

The main body 102 comprises a wireless communication module 106 as afeed circuit that generates a high-frequency signal corresponding to atransmission signal to transmit/receive a radio wave. The wirelesscommunication module 106 is connected to the antenna device 104 via afeed line 107. The feed line 107 is a coaxial cable with a diameter ofabout 1 mm.

With reference to FIG. 2, a description will be given of the circuitryof the notebook PC 100 according to the first embodiment. FIG. 2 is aschematic diagram of the circuitry of the notebook PC 100. The wirelesscommunication module 106 is connected via a CPU bus 200 to a CPU 201 anda memory 202. Although not illustrated, the wireless communicationmodule 106 comprises a radio frequency (RF) module, a crystaloscillator, and a baseband module.

With reference to FIG. 3, a description will be given of a specificconfiguration of the antenna device 104. FIG. 3 is a schematic diagramof the antenna device 104. The antenna device 104 comprises a shortcircuit path 301, a first open-ended element 302, a feed side element303, a second open-ended element 304, a short circuit element 305, and aground conductor (GND) 306.

According to the first embodiment, a ground point 307, i.e., a point onthe GND 306, is arranged near a feed point 309.

A first end of the short circuit path 301 is connected to the groundpoint 307. According to the first embodiment, the short circuit path 301extends from the ground point 307 vertically with respect to the GND306, and then bends and extends parallel to the SND 306.

The first open-ended element 302 is a linear element having an open end,and extends from a second end of the short circuit path 301.

The feed side element 303 is a plate-like element. The feed side element303 is located between the first open-ended element 302 and the GND 306,and extends from the feed point 309 in the direction in which the firstopen-ended element 302 extends. According to the first embodiment, acorner of the feed side element 303 is connected to the feed point 309.

The second open-ended element 304 is a linear element having an openend, and extends from a second end of the feed side element 303 in thedirection in which the first open-ended element 302 extends. Accordingto the first embodiment, the second open-ended element 304 is connectedto a corner of the feed side element 303 diagonally opposite the cornerconnected to the feed point 309.

The short circuit element 305 is a linear element, and connects betweena point on an edge of the feed side element 303 close to a contact point308, i.e., the second end of the feed side element 303, and a first endof the first open-ended element 302. The short circuit element 305 neednot necessarily be located as illustrated in FIG. 3, and may be locatedat different positions. Note that as the point on an edge of the feedside element 303 connected to the short circuit element 305 is closer tothe contact point 308, better antenna characteristics are achieved.

With reference to FIGS. 4 to 7, a description will be given of theoperation principle of the antenna device 104.

FIG. 4 is a schematic diagram for explaining the operation principle ofthe short circuit path 301 and the first open-ended element 302. Theshort circuit path 301 and the first open-ended element 302 causesparallel resonance at a wavelength such that their entire length, fromthe ground point 307 through the short circuit path 301 to a second endof the first open-ended element 302 indicated by an arrow, issubstantially a quarter the wavelength (this parallel resonance ishereinafter referred to as “first parallel resonance”).

FIG. 5 is a schematic diagram for explaining the operation principle ofthe feed side element 303, the short circuit element 305, and the firstopen-ended element 302. The feed side element 303, the short circuitelement 305, and the first open-ended element 302 causes seriesresonance at a first resonant frequency band. More specifically, thefeed side element 303, the short circuit element 305, and the firstopen-ended element 302 resonate at a wavelength such that the length,from the feed point 309 through the outer edge (on the GND 306 side) ofthe feed side element 303 and the short circuit element 305 to thesecond end of the first open-ended element 302 indicated by an arrow, issubstantially a quarter the wavelength (hereinafter this seriesresonance is referred to as “first series resonance”, and the firstresonant frequency indicates the frequency of the first seriesresonance).

FIG. 6 is a schematic diagram for explaining the operation principle ofthe short circuit path 301, the short circuit element 305, and thesecond open-ended element 304. The short circuit path 301, the shortcircuit element 305, and the second open-ended element 304 causesparallel resonance at a wavelength such that their entire length, fromthe ground point 307 through the short circuit path 301 and the shortcircuit element 305 to the second end of the second open-ended element304 indicated by an arrow, is substantially a quarter the wavelength(this parallel resonance is hereinafter referred to as “second parallelresonance”).

FIG. 7 is a schematic diagram for explaining the operation principle ofthe feed side element 303 and the second open-ended element 304. Thefeed side element 303 and the second open-ended element 304 causesseries resonance at a wavelength such that the length, from the feedpoint 309 through the outer edge (on the GND 306 side) of the feed sideelement 303 to the second end of the second open-ended element 304indicated by an arrow, is substantially a quarter the wavelength(hereinafter this series resonance is referred to as “second seriesresonance”, and the frequency of the second series resonance is referredto as “second resonant frequency”)

As described above, according to the first embodiment, the firstparallel resonance and the first series resonance occur in a firstresonant frequency band, and also the second parallel resonance and thesecond series resonance occur in a second resonant frequency band. Thus,the antenna device 104 can create a current distribution similar to thatobtained by the resonance of a folded monopole antenna, and thereforecan exhibit two resonances with high input impedance. Accordingly, evenwhen the antenna device 104 is shortened, favorable input impedance canbe obtained.

Described below is an analytical model of the antenna device 104 and theanalysis results of the antenna characteristics thereof.

With reference to FIGS. 8 and 9, a description will be given of aspecific form of an analytical model to which is applied the antennadevice 104 according to the first embodiment. FIG. 8 is a diagramillustrating a specific form of the analytical model. The analyticalmodel of FIG. 8 is designed such that the first resonant frequency bandis about 1.8 GHz and the second resonant frequency band is about 900MHz. FIG. 9 is a diagram illustrating the form of the GND 306 of theanalytical model. All the following analysis results are the results ofthe Method of Moment.

The short circuit path 301 extends from the ground point 307 verticallywith respect to the GND 306, and then bends and extends parallel to theGND 306. The first open-ended element 302 extends from the second end ofthe short circuit path 301. The feed side element 303 is a plate-likeelement, and a corner of which is connected to the feed point 309. Thesecond open-ended element 304 is connected to a corner of the feed sideelement 303 diagonally opposite the corner connected to the feed point309. The second open-ended element 304 has an open end, and extends inthe direction in which the first open-ended element 302 extends. Theshort circuit element 305 connects between a point close to the contactpoint 308 and the first end of the first open-ended element 302. Theshort circuit element 305 extends vertically with respect to the GND306.

It is assumed in this analytical model that the GND 306 has a length of100 mm in the direction in which the short circuit path 301 extends, anda length of 200 mm in the direction perpendicular to the direction inwhich the short circuit path 301 extends.

With reference to FIGS. 10 to 14, a description will be given of theantenna characteristics of the analytical model of FIGS. 8 and 9. FIG.10 is a Smith chart of the antenna characteristics of the analyticalmodel of FIGS. 8 and 9. FIGS. 11 to 14 are schematic diagrams forexplaining an antenna realized by the analytical model of FIGS. 8 and 9.The Smith chart of FIG. 10 represents the impedance variation of theanalytical model when the frequency signal fed from the feed point 309is changed in a range of 700 to 2500 MHz.

As illustrated in FIG. 10, the plot of the impedance of the analyticalmodel crosses the horizontal axis of the Smith chart at (2) 1720 MHz.This represents the occurrence of the first parallel resonance indicatedby an arrow in FIG. 11. Similarly, the plot of the impedance of theanalytical model crosses the horizontal axis of the Smith chart at (1)1810 MHz. This represents the occurrence of the first series resonanceindicated by an arrow in FIG. 12.

As just described, with this analytical model, the first parallelresonance and the first series resonance occur at nearby frequencies.Thus, the input impedance at the first resonant frequency can beincreased.

In addition, the plot of the impedance of the analytical model crossesthe horizontal axis of the Smith chart at (4) 830 MHz. This representsthe occurrence of the second parallel resonance indicated by an arrow inFIG. 13. Similarly, the plot of the impedance of the analytical modelcrosses the horizontal axis of the Smith chart at (3) 920 MHz. Thisrepresents the occurrence of the second series resonance indicated by anarrow in FIG. 14.

As just described, with this analytical model, the second parallelresonance and the second series resonance occur at nearby frequencies.Thus, the input impedance at the second resonant frequency can beincreased. Moreover, in the band of the second resonant frequency (thesecond resonant frequency band), the plot on the Smith chart passes thecenter of the chart, i.e., around 50Ω. Therefore, the second resonantfrequency band can be widened.

With reference to FIGS. 15 to 17, a description will be given of theresults of comparison between the analytical model having the feed sideelement 303 and that of a conventional antenna device 1600 not havingthe feed side element 303. The conventional antenna device 1600 is ofbasically the same form as the antenna device 104 except for the absenceof the feed side element 303, and will not be described in detail. FIG.15 is a Smith chart of the input impedance of the analytical modelhaving the feed side element 303 and one not having the feed sideelement 303 at frequencies of 700 to 2500 MHz.

As illustrated in FIG. 15, with respect to the analytical model of theconventional antenna device 1600 that is not provided with the feed sideelement 303 as illustrated in FIG. 16, the plot on the Smith chartdeviates upward from the centre of the chart, i.e., around 50Ω. This isbecause the inductivity of the input impedance increases due to current1001 flowing from the feed point 309 through the short circuit element305 and the short circuit path 301 to the ground point 307 asillustrated in FIG. 16.

On the other hand, as illustrated in FIG. 15, with respect to theanalytical model of the antenna device 104 that is provided with thefeed side element 303, the plot is drawn in the centre of the Smithchart, i.e., around 50Ω, compared to the analytical model of theconventional antenna device 1600. This indicates that current 1701,which flows from the feed point 309 through the outer edge (on the sideopposite the GND 306 side) of the feed side element 303, the shortcircuit element 305 and the short circuit path 301 to the ground point307 as illustrated in FIG. 17, is smaller than the current 1001, andthus the inductivity of the input impedance is low. As a result,favorable impedance matching can be achieved.

As described above, according to the first embodiment, with the feedside element 303, the inductivity of the input impedance of the antennadevice 104 can be lower compared to an antenna device not provided withthe feed side element 303. Thus, favorable impedance matching can beachieved in the band of each resonant frequency.

If the antenna device as described in the first embodiment is suppliedwith power via a coaxial cable, the feed line, i.e., a coaxial cable,can be prevented from adversely affecting the characteristics of theantenna device by grounding the short circuit path connected to theouter conductor of the feed line. Such an antenna device will bedescribed as an modification of the first embodiment. The antenna deviceof the modification is of basically the same configuration as previouslydescribed in the first embodiment, and thus only the difference from thefirst embodiment will be described.

FIG. 18 is a schematic diagram of an antenna device 2000 according tothe modification. With reference to FIG. 18, a description will be givenof how to attach the feed line to the antenna device 2000.

In the antenna device 2000 of the modification, the short circuit path301 is connected to an outer conductor 2001 of the feed line 107 that isa coaxial cable for supplying power to the feed point 309. According tothe modification, the short circuit path 301 is soldered to the outerconductor 2001. As just described, since the feed line 107 is connectedto the feed point 309 inside the antenna device 2000, extra space is notrequired for soldering and grounding of the outer conductor 2001.Therefore, the antenna device 2000 needs less space for installation.Moreover, the short circuit path 301 is connected to the outer conductor2001 of the feed line 107 and led out in a direction separate from theantenna device 2000. This prevents the feed line 107 from being locatedclose to the antenna device 2000. Thus, the feed line 107 can beprevented from adversely affecting the characteristics of the antennadevice 2000.

Described below is an antenna device according to a second embodiment ofthe invention. In the second embodiment, the feed point is spaced apartfrom the ground point by an appropriate distance. The antenna device ofthe second embodiment is of basically the same configuration aspreviously described in the first embodiment, and thus only thedifference from the first embodiment will be described.

The feed point 309 is spaced apart from the ground point 307 in thedirection in which the first open-ended element 302 extends. Thedistance between the feed point 309 and the ground point 307 is equal toor less than substantially a twentieth of the wavelength of the lowerone of the first resonant frequency or the second resonant frequency.For example, if the second resonant frequency is 910 MHz which is lowerthan the first resonant frequency, the feed point 309 is spaced apartfrom the ground point 307 by a distance equal to or less than 16 mm,substantially a twentieth of wavelength λ=330 mm.

In the following, a description will be given of analytical models ofthe antenna device 104 according to the second embodiment and results ofanalysis on the antenna characteristics.

With reference to FIGS. 19 and 20, a description will first be given ofthree analytical models the antenna characteristics of which areanalyzed. FIG. 19 is a schematic diagram of an analytical model of theantenna device 104 comprising the short circuit path. The analyticalmodel of FIG. 19 is designed such that the first resonant frequency bandis about 1.8 GHz and the second resonant frequency band is about 900MHz. FIG. 20 is a schematic diagram of an analytical model of an antennadevice 2200 having no short circuit path. The analytical models arebasically similar to that of the antenna device according to the firstembodiment except for the distance between the feed point 309 and theground point 307. Therefore, their description will not be repeated.

In the first analytical model illustrated in FIG. 19, the feed point 309is spaced apart from the ground point 307 by a distance a=1 mm on theGND 306. The second analytical model of the antenna device 2200 is notprovided with the short circuit path 301 as can be seen from FIG. 20. Inthe third analytical model illustrated in FIG. 19, the feed point 309 isspaced apart from the ground point 307 by a distance a=16 mm on the GND306.

With reference to FIG. 21, a description will then be given of theantenna characteristics of the above analytical models. The Smith chartof FIG. 21 represents the impedance variation of the analytical modelsof FIGS. 19 and 20 when the frequency signal fed from the feed point 309is changed in a range of 700 to 1200 MHz.

The plot of the impedance of the first analytical model (a=1 mm) crossesthe horizontal axis of the Smith chart at 910 MHz. At the cross point,the impedance is about 34Ω, which is close to 50Ω at the center of theSmith chart. This is because, in the first analytical model (a=1 mm),the second parallel resonance illustrated in FIG. 13 and the secondseries resonance illustrated in FIG. 14 occur at nearby frequencies.

The plot of the impedance of the second analytical model crosses thehorizontal axis of the Smith chart at 930 MHz. At the cross point, theimpedance is about 18Ω, which is far from 50Ω at the center of the Smithchart compared to the first analytical model (a=1 mm). This is because,in the second analytical model (FIG. 20), the second parallel resonanceillustrated in FIG. 13 does not occur, and the current distribution issimilar to a monopole antenna.

The plot of the impedance of the third analytical model (a=16 mm)crosses the horizontal axis of the Smith chart at 930 MHz. At the crosspoint, the impedance is about 26Ω, which is far from 50Ω at the centerof the Smith chart compared to the impedance of the second resonantfrequency of the first analytical model. This is because, in the thirdanalytical model (a=16 mm), the path to determine the frequency of thesecond parallel resonance illustrated in FIG. 13 is long compared to thefirst analytical model (a=1 mm). As a result, the second parallelresonance occurs at a frequency far from that of the second seriesresonance illustrated in FIG. 14.

According to the analysis results described above, the impedance (26Ω)of the third analytical model (a=16 mm) at the cross point on thehorizontal axis of the Smith chart is substantially intermediate betweenthe impedance (34Ω) of the first analytical model (a=1 mm) and theimpedance (18Ω) of the second analytical model (without the shortcircuit path 301). Therefore, according to the second embodiment, thethird analytical model is used as a reference. Since a=16 mm is a valuesubstantially a twentieth of wavelength λ=330 mm of the second resonantfrequency (910 MHz), the feed point 309 is spaced apart from the groundpoint 307 by a distance equal to or less than substantially a twentiethof wavelength λ of the second resonant frequency.

Described below is an antenna device according to a third embodiment ofthe invention. In the third embodiment, the length of the feed sideelement is adjusted to be appropriate in the direction in which thefirst open-ended element 302 extends to thereby lower the inductivity ofthe input impedance. The antenna device of the third embodiment is ofbasically the same configuration as the antenna device of the secondembodiment, and thus only the difference between the two will bedescribed.

FIG. 22 is a schematic diagram of the antenna device according to thethird embodiment. It is assumed that the feed side element 303 has alength b in the direction in which the first open-ended element 302extends that is equal to or more than substantially a fiftieth of thewavelength of the second resonant frequency. If, for example, the secondresonant frequency is 865 MHz, the length b, i.e., the length from thefeed point 309 in the direction in which the first open-ended element302 extends (parallel to the GND 306), of the feed side element 303 is 7mm, substantially a fiftieth of wavelength λ=346 mm of the secondresonant frequency.

In the following, a description will be given of analytical models ofthe antenna device 104 having different lengths b and results ofanalysis on the antenna characteristics.

With reference to FIG. 23, a description will first be given of threeanalytical models the antenna characteristics of which are analyzed.FIG. 23 is a diagram illustrating a specific form of the analyticalmodels. The analytical models of FIG. 23 are designed such that thefirst resonant frequency band is about 1.8 GHz and the second resonantfrequency band is about 900 MHz. The analytical models are basicallysimilar to that of the antenna device according to the second embodimentexcept for the form of the feed side element 303. Therefore, theirdescription will not be repeated.

In the first analytical model, the length b of the feed side element 303is 5 mm. In the second analytical model, the length b of the feed sideelement 303 is 6 mm. In the third analytical model, the length b of thefeed side element 303 is 7 mm.

With reference to FIG. 24, a description will then be given of theantenna characteristics of the above analytical models. The Smith chartof FIG. 24 represents the impedance variation of the analytical modelsof FIG. 23 when the frequency signal fed from the feed point 309 ischanged in a range of 700 to 1200 MHz.

The plots of the impedance of the first analytical model (b=5 mm) andthe second analytical model (b=6 mm) deviate upward and do not cross thehorizontal axis of the Smith chart. This is because the feed sideelement 303 does not have a sufficient length in the direction in whichthe first open-ended element 302 extends. Therefore, as with aconventional antenna device formed of linear elements, the effect of thecurrent flowing from the feed point 309 to the ground point 307 is notsufficiently suppressed, which results in high inductivity of the inputimpedance. On the other hand, the plot of the impedance of the thirdanalytical model (b=7 mm) crosses the horizontal axis of the Smith chartat 840 MHz and 860 MHz. This represents the occurrence of the secondparallel resonance illustrated in FIG. 13 and the second seriesresonance illustrated in FIG. 14

It can be seen from the analysis results described above that theinductivity of the input impedance decreases as the length b of the feedside element 303 increases. Therefore, according to the thirdembodiment, the third analytical model is used as a reference. Since b=7mm is a value substantially a fiftieth of wavelength λ=365 mm of thesecond resonant frequency (865 MHz), the length b, i.e., the length fromthe feed point 309 in the direction in which the first open-endedelement 302 extends (parallel to the GND 306), of the feed side element303 is adjusted to be equal to or more than substantially a fiftieth ofthe wavelength of the second resonant frequency.

Described below is an antenna device according to a fourth embodiment ofthe invention. In the fourth embodiment, the contact point, i.e., thesecond end of the feed side element, and the first end of the firstopen-ended element are connected via the short circuit element toprevent the input impedance from excessively rising and thereby to widenthe band of the first resonant frequency (the first resonant frequencyband). The antenna device of the fourth embodiment is of basically thesame configuration as the antenna device of the third embodiment, andthus only the difference between the two will be described.

FIG. 25 is a schematic diagram of the antenna device according to thefourth embodiment. The short circuit element 305 connects between thecontact point 308, i.e., the second end of the feed side element 303 andthe first end of the first open-ended element 302.

In the following, a description will be given of analytical models ofthe antenna device 104 in which the short circuit element 305 isconnected to different positions, and results of analysis on the antennacharacteristics.

With reference to FIGS. 26 to 28, a description will first be given ofthree analytical models the antenna characteristics of which areanalyzed. FIGS. 26 to 28 are diagrams of specific forms of theanalytical models. The analytical models of FIGS. 26 to 28 are designedsuch that the first resonant frequency band is about 1.8 GHz and thesecond resonant frequency band is about 900 MHz. The analytical modelsare basically similar to that of the antenna device according to thethird embodiment except for the position to which the short circuitelement 305 is connected (connection position). Therefore, theirdescription will not be repeated.

In the analytical model of FIG. 26, the length of the short circuit path301 is reduced in the direction in which the first open-ended element302 extends to shift the connection position of the short circuitelement 305 from the contact point 308 side to the short circuit path301 side. In the analytical model of FIG. 27, the length of the shortcircuit path 301 is increased in the direction in which the firstopen-ended element 302 extends to shift the connection position of theshort circuit element 305 from the contact point 308 side to the firstopen-ended element 302 side. In the analytical model of FIG. 28, theshort circuit element 305 is connected to the contact point 308.

With reference to FIGS. 29 to 31, a description will then be given ofthe results of analysis on the antenna characteristics of the analyticalmodels illustrated in FIGS. 26 to 28. FIG. 29 is a schematic diagram forexplaining resonance that occurs in the analytical model of FIG. 26.FIG. 30 is a schematic diagram for explaining resonance that occurs inthe analytical model of FIG. 27. FIG. 31 is a graph of results ofanalysis on voltage standing wave ratio (VSWR) characteristics over thefirst resonant frequency band in the analytical models of FIGS. 26 to28.

With reference to FIG. 29, a description will be given of the inputimpedance characteristics of the first resonant frequency band in theanalytical model of FIG. 26. As the connection position of the shortcircuit element 305 shifts from the contact point 308 side to the shortcircuit path 301 side, the frequency of the first parallel resonance andthat of the first series resonance become too close to each other asillustrated in FIG. 29. Consequently, the input impedance over the firstresonant frequency band excessively rises, resulting in a narrowcoverage band.

With reference to FIG. 30, a description will be given of the inputimpedance characteristics of the first resonant frequency band in theanalytical model of FIG. 27. As the connection position of the shortcircuit element 305 shifts from the contact point 308 side to the firstopen-ended element 302 side, the frequency of third parallel resonanceand that of the first series resonance become too close to each other asillustrated in FIG. 30. Consequently, the input impedance over the firstresonant frequency band excessively rises, resulting in a narrowcoverage band.

As described above, the first resonant frequency band is affected by thefirst parallel resonance, the first series resonance, and the thirdparallel resonance depending on the connection position of the shortcircuit element 305. By setting the connection position of the shortcircuit element 305 near the contact point 308, a favorable balance isachieved between the first parallel resonance, the first seriesresonance and the third parallel resonance, and the first resonantfrequency band can be widened.

It can be seen from the VSWR characteristics illustrated in FIG. 31 thatthe VSWR is lower and the first resonant frequency band is wider for theanalytical model of FIG. 28 compared to the analytical models of FIGS.26 and 27. This indicates that, by setting the connection position ofthe short circuit element 305 near the contact point 308, the firstresonant frequency band widens.

Described below is an antenna device according to a fifth embodiment ofthe invention. In the fifth embodiment, the distance between the edge ofthe feed side element on the GND side and the GND is changed to adjustthe inductivity of the input impedance. The antenna device of the fifthembodiment is of basically the same configuration as the antenna deviceof the fourth embodiment, and thus only the difference between the twowill be described.

FIG. 32 is a schematic diagram of the antenna device according to thefifth embodiment. The feed side element 303 is located between the firstopen-ended element 302 and the GND 306, and is spaced apart from the GND306 by a distance c equal to or less than substantially a hundredth ofthe wavelength of the second resonant frequency. For example, if thesecond resonant frequency is 860 MHz, the feed side element 303 extendssubstantially parallel to the GND 306 with a space therebetween equal toor less than 3 mm, substantially a hundredth of wavelength λ=348 mm.

In the following, a description will be given of analytical models ofthe antenna device 104 having different distances c and results ofanalysis on the antenna characteristics.

With reference to FIG. 33, a description will first be given of threeanalytical models the antenna characteristics of which are analyzed.FIG. 33 is a diagram illustrating a specific form of the analyticalmodels. The analytical models of FIG. 33 are designed such that thefirst resonant frequency band is about 1.8 GHz and the second resonantfrequency band is about 900 MHz. The analytical models are basicallysimilar to that of the antenna device according to the fourth embodimentexcept for the distance between the feed side element 303 and the GND306. Therefore, their description will not be repeated.

In the first analytical model, the distance c is 1 mm. In the secondanalytical model, the distance c is 2 mm. In the third analytical model,the distance c is 3 mm.

With reference to FIG. 34, a description will then be given of theantenna characteristics of the above analytical models. The Smith chartof FIG. 34 represents the impedance variation of the analytical modelsof FIG. 33 when the frequency signal fed from the feed point 309 ischanged in a range of 700 to 1200 MHz.

The plot of the impedance of the first analytical model (c=1 mm) crossesthe horizontal axis of the Smith chart at (1) 860 MHz and (2) 840 MHz.This represents the occurrence of the second parallel resonance and thesecond series resonance. The plot of the impedance of the secondanalytical model (c=2 mm) crosses the horizontal axis of the Smith chartat (3) 855 MHz and (2) 835 MHz. This also represents the occurrence ofthe second parallel resonance and the second series resonance. On theother hand, the plot of the impedance of the third analytical model (c=3mm) does not cross the horizontal axis of the Smith chart, and gives noindication of the occurrence of the second parallel resonance and thesecond series resonance.

As just described, by reducing the distance between the feed sideelement 303 and the GND 306, the inductivity of the input impedance ofthe antenna device can be lowered (the capacitance can be increased),and thus favorable impedance characteristics can be obtained in thefirst and second resonant frequency bands. According to the fifthembodiment, the third analytical model is used as a reference. Since c=3mm is a value substantially a hundredth of wavelength λ=348 mm of thesecond resonant frequency (860 MHz), the feed side element 303 is spacedapart from the GND 306 by a distance equal to or less than substantiallya hundredth of the wavelength of the second resonant frequency.

Described below is an antenna device 3800 according to a sixthembodiment of the invention. The antenna device 3800 further comprisinga parasitic element 3801 near the feed side element 303 increases itsresonant frequencies. Otherwise, the antenna device 3800 is of basicallythe same configuration as the antenna device of the fifth embodiment,and thus only the difference between the two will be described.

FIG. 35 is a schematic diagram of the antenna device 3800 according tothe sixth embodiment. As illustrated in FIG. 35, the antenna device 3800is provided with the parasitic element 3801 between the secondopen-ended element 304 and the GND 306.

In the following, a description will be given of an analytical model ofthe antenna device 3800 according to the sixth embodiment and results ofanalysis on the antenna characteristics.

With reference to FIG. 36, a description will first be given of theanalytical model the antenna characteristics of which are analyzed. FIG.36 is a schematic diagram of the analytical model of the antenna device3800 further comprising the parasitic element. The analytical model ofFIG. 36 is designed such that the first resonant frequency band is about1.8 GHz and the second resonant frequency band is about 900 MHz. Theanalytical model is basically similar to that of the antenna deviceaccording to the fifth embodiment except for the presence of theparasitic element 3801. Therefore, its description will not be repeated.

The parasitic element 3801 extends from a position near the feed sideelement 303 vertically with respect to the GND 306, then bends, andextends parallel to the GND 306. In other words, the parasitic element3801 extends in the direction in which the second open-ended element 304extends.

With reference to FIGS. 37 and 38, a description will then be given ofthe antenna characteristics of an analytical model having no parasiticelement and the analytical model of FIG. 36 having the parasiticelement. FIG. 37 is a graph of results of analysis on VSWRcharacteristics of the analytical model having no parasitic element andone having the parasitic element. The Smith chart of FIG. 38 representsthe impedance variation of the analytical models of FIG. 37 when thefrequency signal fed from the feed point 309 is changed in a range of700 to 2500 MHz.

With reference to FIG. 37, a description will be given of the results ofanalysis on VSWR characteristics of the analytical model having noparasitic element and the analytical model of the antenna device 3800having the parasitic element 3801 illustrated in FIG. 36. As illustratedin FIG. 37, for both the analytical model having no parasitic elementand the analytical model of the antenna device 3800 having the parasiticelement 3801, the VSWR is low at the second resonant frequency band(about 0.9 GHz) as well as the first resonant frequency band (about 1.8GHz). This indicates that favorable input impedance can be obtained atthe respective resonant frequencies. Further, for the analytical modelof the antenna device 3800 having the parasitic element 3801, the VSWRis low at a new resonant frequency band (about 2.2 GHz). This indicatesan increase in the number of resonant frequencies due to the parasiticelement 3801.

Besides, referring to FIG. 38, for the analytical model having noparasitic element, there are two series resonance points on the plot onthe Smith chart. On the other hand, for the analytical model of theantenna device 3800 having the parasitic element 3801, there are threeseries resonance points on the plot on the Smith chart. This alsoindicates an increase in the number of resonant frequencies due to theparasitic element 3801.

As described above, according to the sixth embodiment, the antennadevice further comprises the parasitic element near the feed sideelement. Thus, the number of resonant frequencies increases, and theantenna device can further be of multiple resonance.

Described below is an antenna device 4200 according to a seventhembodiment of the invention. The antenna device 4200 comprise, in placeof the short circuit path 301, a short circuit path 4201 having aprojection to adjust the resonant frequencies and the input impedance atthe resonant frequencies. Otherwise, the antenna device 4200 is ofbasically the same configuration as the antenna device of the fifthembodiment, and thus only the difference between the two will bedescribed.

With reference to FIG. 39, a description will be given of the antennadevice 4200 provided with the short circuit path 4201 having such aprojection. FIG. 39 is a schematic diagram of the antenna device 4200comprising the short circuit path 4201 having a projection 4201 a.

The short circuit path 4201 of the antenna device 4200 according to theseventh embodiment bends at at least three points to form the projection4201 a on a part thereof. More specifically, according to the seventhembodiment, the short circuit path 4201 bends at three points to formthe projection 4201 a on a part thereof that extends vertically from theground point 307 with respect to the GND 306.

In the following, a description will be given of an analytical model ofthe antenna device 4200 according to the seventh embodiment and resultsof analysis on the antenna characteristics with reference to FIGS. 40and 41. FIG. 40 is a diagram of a specific form of an analytical modelof the antenna device 4200 provided with the short circuit path 4201having the projection 4201 a. The analytical model of FIG. 40 isdesigned such that the first resonant frequency band is about 1.8 GHzand the second resonant frequency band is about 900 MHz. The Smith chartof FIG. 41 represents the input impedance of the analytical model ofFIG. 40 at 700 to 2500 MHz.

With reference to FIG. 40, a description will first be given of theanalytical model the antenna characteristics of which are analyzed. Theanalytical model is basically similar to that of the antenna deviceaccording to the sixth embodiment except for the short circuit path4201. Therefore, its description will not be repeated. As illustrated inFIG. 40, the short circuit path 4201 extends vertically from the groundpoint 307 with respect to the GND 306, and then bends in the directionopposite the direction in which the first open-ended element 302extends. The short circuit path 4201 bends and extends again verticallywith respect to the GND 306, and bends once more to form the projection4201 a.

With reference to FIG. 41, a description will then be given of theantenna characteristics of the analytical model of FIG. 40. It can beseen from FIG. 41 that, for the analytical model provided with theprojection, the plot on the Smith chart is close to the center of thechart, i.e., 50Ω, compared to the plot for the analytical model providedwith no such a projection. It can also be seen from FIG. 41 that theplot of the impedance of the analytical model with no projection crossesthe horizontal axis of the Smith chart due to neither the first parallelresonance illustrated in FIG. 11 nor the first series resonanceillustrated in FIG. 12. On the other hand, the plot of the impedance ofthe analytical model with the projection crosses the horizontal axis ofthe Smith chart due to the first parallel resonance illustrated in FIG.11 and the first series resonance illustrated in FIG. 12.

As described above, according to the seventh embodiment, a projection isformed on a part of the short circuit path, which enables adjustment ofthe length of the short circuit path. By adjusting the length of theshort circuit path, it is possible to adjust the frequencies of thefirst parallel resonance and the second parallel resonance and therebyto adjust the input impedance characteristics over the first and secondresonant frequency bands.

Described below is an antenna device 4500 according to an eighthembodiment of the invention. FIG. 42 is a schematic diagram of theantenna device 4500 comprising a short circuit path 4501 provided withan impedance matching circuit 4501 a according to the eighth embodiment.

In the antenna device 4500 of the eighth embodiment, the impedancematching circuit 4501 a, such as a chip inductor, is provided on theshort circuit path 4501. The value of the chip inductor is adjusted toadjust the first and second resonant frequencies as well as the inputimpedance at the resonant frequencies.

In the following, a description will be given of an analytical model ofthe antenna device 4500 according to the eighth embodiment and resultsof analysis on the antenna characteristics with reference to FIGS. 43and 44. FIG. 43 is a diagram of a specific form of an analytical modelof the antenna device 4500 provided with the short circuit path 4501 onwhich is arranged the impedance matching circuit 4501 a. The analyticalmodel of FIG. 43 is designed such that the first resonant frequency bandis about 1.8 GHz and the second resonant frequency band is about 900MHz. The Smith chart of FIG. 44 represents the input impedance of theanalytical model of FIG. 43 at 700 to 2500 MHz.

With reference to FIG. 43, a description will first be given of theanalytical model the antenna characteristics of which are analyzed. Theanalytical model is basically similar to that of the antenna deviceaccording to the sixth embodiment except for the short circuit path4501. Therefore, its description will not be repeated. As illustrated inFIG. 46, the short circuit path 4501 is provided with a chip inductor(L=5 nH), i.e., the impedance matching circuit 4501 a, on its pathextending vertically from the ground point 307 with respect to the GND306.

With reference to FIG. 44, a description will then be given of theantenna characteristics of the analytical model of FIG. 43. It can beseen from FIG. 44 that, for the analytical model provided with the chipinductor on the path, the plot on the Smith chart is close to the centerof the chart, i.e., 50Ω, compared to the plot for the analytical modelprovided with no chip inductor. It can also be seen from FIG. 44 thatthe plot of the impedance of the analytical model with no chip inductorcrosses the horizontal axis of the Smith chart due to neither the firstparallel resonance illustrated in FIG. 11 nor the first series resonanceillustrated in FIG. 12. On the other hand, the plot of the impedance ofthe analytical model with the chip inductor crosses the horizontal axisof the Smith chart due to the first parallel resonance illustrated inFIG. 11 and the first series resonance illustrated in FIG. 12.

As described above, according to the eighth embodiment, a chip inductoris arranged on the short circuit path. By adjusting the value of thechip inductor, the same effect can be achieved as in the case where aprojection is formed on the short circuit path and thereby the lengththereof is adjusted. That is, with the impedance matching circuitprovided on the short circuit path, it is possible to adjust the firstand second resonant frequencies as well as the input impedance at theresonant frequencies by adjusting the value of the impedance matchingcircuit.

With reference to FIGS. 45A to 45L, a description will be given ofmodifications of the embodiments described above. FIGS. 45A to 45L areschematic diagrams of antenna devices according to modifications of thefirst to eighth embodiments. The antenna devices according to themodifications are of basically the same configuration as previouslydescribed in the above embodiments, and thus only the difference fromthe above embodiments will be described.

FIG. 45A illustrates a modification of the antenna device comprising afirst open-ended element 4800 that is longer than the second open-endedelement 304 in the direction in which they extend. FIG. 45B illustratesanother modification of the antenna device further comprising an antennaelement 4801 that requires power supply. FIG. 45C illustrates stillanother modification of the antenna device in which the secondopen-ended element 304 does not extend from the contact point 308 at acorner of the feed side element 303 but extends from a point 4802 on anedge of the feed side element 303. FIG. 45D illustrates still anothermodification of the antenna device comprising a feed side element 4803in a distorted shape. FIG. 45E illustrates still another modification ofthe antenna device comprising a plate-like short circuit element 4804.FIG. 45F illustrates still another modification of the antenna devicecomprising a linear feed side element 4805. FIG. 45G illustrates stillanother modification of the antenna device comprising a feed sideelement 4806 in a trapezoidal shape. FIG. 45H illustrates still othermodifications of the antenna device, one comprising a second open-endedelement 4807 in a bent shape, the other comprising a first open-endedelement 4808 in a bent shape. FIG. 45I illustrates still othermodifications of the antenna device, one comprising a first open-endedelement 4809 in a meander shape, the other comprising a secondopen-ended element 4810 in a meander shape. FIG. 45J illustrates stillanother modification of the antenna device comprising a short circuitpath 4811 that is longer than the short circuit path 4201 of the seventhembodiment and is bent. FIG. 45K illustrates still another modificationin which the antenna device of the first to eighth embodiments is foldedaccording to the shape of the housing and is attached thereto. FIG. 45Lillustrates still another modification of the antenna device in whichthe feed point 309 is not arranged at a corner of the feed side element303 but is arranged on an edge thereof on the GND 306 side.

With reference to FIGS. 46 and 47, a description will be given of anantenna device 4900 as a specific example of the antenna deviceaccording to the embodiments described above. FIG. 46 is a diagram of aspecific form of the antenna device 4900. FIG. 47 is a graph of resultsof analysis on VSWR characteristics of the antenna device 4900.

With reference to FIG. 46, a description will first be given of theconfiguration of the antenna device 4900. The antenna device 4900comprises a short circuit path 4901 r a first open-ended element 4902, afeed side element 4903, a second open-ended element 4904, a shortcircuit element 4905, a GND 4906, and a parasitic element 4910. Theshort circuit path 4901 extends from a ground point 4907 and has anL-shaped bent portion. The first open-ended element 4902 is connected toa second end of the short circuit path 4901 and is bent in an opensquare shape. The feed side element 4903 is a plate-like element, acorner of which is connected to a feed point 4909. The second open-endedelement 4904 is connected to a contact point 4908 at a corner of thefeed side element 4903 diagonally opposite the corner connected to thefeed point 4909. The short circuit element 4905 connects between a firstend of the first open-ended element 4902 and the second open-endedelement 4904. The parasitic element 4910 is located between the secondopen-ended element 4904 and the GND 4906.

With reference to FIG. 47, a description will then be given of resultsof analysis on VSWR characteristics of the antenna device 4900.

As illustrated in FIG. 47, the antenna device 4900 achieves VSWR equalto or lower than 3 in the resonant frequency bands of the first resonantfrequency (about 1.8 GHz), the second resonant frequency (about 0.9GHz), and the third resonant frequency (about 2.3 GHz). This indicatesthat favorable input impedance characteristics can be obtained at eachof the resonant frequencies.

As described above, the antenna device 4900 can achieve the same effectas previously described in the above embodiments. The antenna device4900 is a planar antenna in which is formed a planar pattern ofelements, and is designed for use in third generation mobile phonehandsets. The antenna device 4900 covers the 800 MHz band (825 to 960MHz) and the 2 GHz band (1710 to 2170 MHz).

With reference to FIGS. 48 and 49, a description will be given of anantenna device 5200 as another specific example of the antenna deviceaccording to the embodiments described above. FIG. 48 is a diagram of aspecific form of the antenna device 5200. FIG. 49 is a graph of resultsof analysis on VSWR characteristics of the antenna device 5200.

With reference to FIG. 48, a description will first be given of theconfiguration of the antenna device 5200. The antenna device 5200comprises a short circuit path 5201, a first open-ended element 5202, afeed side element 5203, a second open-ended element 5204, a shortcircuit element 5205, a GND 5206, and a parasitic element 5210. Theshort circuit path 5201 is provided with a chip inductor 5201 a (L=5 nH)on a portion extending from a ground point 5207. The first open-endedelement 5202 is connected to a second end of the short circuit path5201. The feed side element 5203 is a plate-like element, a corner ofwhich is connected to a feed point 5209. The second open-ended element5204 is connected to a contact point 5208 at a corner of the feed sideelement 5203 diagonally opposite the corner connected to the feed point5209. The short circuit element 5205 connects between a first end of thefirst open-ended element 5202 and a point on an edge of the feed sideelement 5203 close to the contact point 5208. The parasitic element 5210is located between the second open-ended element 5204 and the GND 5206.

With reference to FIG. 49, a description will then be given of resultsof analysis on VSWR characteristics of the antenna device 5200.

As illustrated in FIG. 49, the antenna device 5200 achieves VSWR equalto or lower than 3 in the resonant frequency bands of the first resonantfrequency (about 1.8 GHz), the second resonant frequency (about 0.9GHz), and the third resonant frequency (about 2.3 GHz). This indicatesthat favorable input impedance characteristics can be obtained at eachof the resonant frequencies.

As described above, the antenna device 5200 can achieve the same effectas previously described in the above embodiments. The antenna device5200 is a planar antenna in which is formed a planar pattern ofelements, and is designed for use in third generation mobile phonehandsets. The antenna device 5200 covers the 800 MHz band (825 to 960MHz) and the 2 GHz band (1710 to 2170 MHz).

The various modules of the systems described herein can be implementedas software applications, hardware and/or software modules, orcomponents on one or more computers, such as servers. While the variousmodules are illustrated separately, they may share some or all of thesame underlying logic or code.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the inventions. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the inventions. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the inventions.

1. An antenna device comprising: a short circuit path a first end ofwhich is connected to a ground point that is located near a feed point;a first open-ended element that has a second end being open, and extendsfrom a second end of the short circuit path; a feed side element thatextends from near the feed point in a direction in which the firstopen-ended element extends to have an edge close to ground; a secondopen-ended element that has a second end being open, and extends fromnear a second end of the feed side element in the direction in which thefirst open-ended element extends; and a short circuit element thatconnects between a first end of the first open-ended element and eithera point on an edge of the feed side element opposite the edge close tothe ground or a point on the second open-ended element, wherein alength, from the feed point through an outer edge of the feed sideelement including the edge close to the ground and the short circuitelement to the second end of the first open-ended element, issubstantially a quarter of a wavelength of a first resonant frequency,and a length, from the feed point through the outer edge of the feedside element including the edge close to the ground to the second end ofthe second open-ended element, is substantially a quarter of awavelength of a second resonant frequency.
 2. The antenna device ofclaim 1, wherein the feed point is spaced apart from the ground point inthe direction in which the first open-ended element extends by adistance equal to or less than substantially a twentieth of thewavelength of lower one of the first resonant frequency or the secondresonant frequency.
 3. The antenna device of claim 1, wherein the feedside element has a length equal to or more than substantially a fiftiethof the wavelength of lower one of the first resonant frequency or thesecond resonant frequency in the direction in which the first open-endedelement extends.
 4. The antenna device of claim 1, wherein the shortcircuit element connects between the first end of the first open-endedelement and the point near the second end of the feed side element. 5.The antenna device of claim 1, wherein the feed side element is locatedbetween the first open-ended element and a ground conductor, and theedge of the feed side element close to the ground is spaced apart fromthe ground conductor by a distance equal to or less than substantially ahundredth of the wavelength of lower one of the first resonant frequencyor the second resonant frequency.
 6. The antenna device of claim 1,further comprising a parasitic element near the feed side element. 7.The antenna device of claim 1, wherein the short circuit path bends atat least three points to form a projection on a part of the shortcircuit path.
 8. The antenna device of claim 1, further comprising animpedance matching circuit on the short circuit path.
 9. The antennadevice of claim 4, wherein the short circuit element connects betweenthe first end of the first open-ended element and a contact point at thesecond end of the feed side element.
 10. Electronic equipment comprisinga housing having a built-in antenna device, the antenna devicecomprising: a short circuit path a first end of which is connected to aground point that is located near a feed point; a first open-endedelement that has a second end being open, and extends from a second endof the short circuit path; a feed side element that extends from nearthe feed point in a direction in which the first open-ended elementextends to have an edge close to ground; a second open-ended elementthat has a second end being open, and extends from near a second end ofthe feed side element in the direction in which the first open-endedelement extends; and a short circuit element that connects between afirst end of the first open-ended element and either a point on an edgeof the feed side element opposite the edge close to the ground or apoint on the second open-ended element, wherein a length, from the feedpoint through an outer edge of the feed side element including the edgeclose to the ground and the short circuit element to the second end ofthe first open-ended element, is substantially a quarter of a wavelengthof a first resonant frequency, and a length, from the feed point throughthe outer edge of the feed side element including the edge close to theground to the second end of the second open-ended element, issubstantially a quarter of a wavelength of a second resonant frequency.